1. Field of the Invention
The present invention relates to silica containing dentifrice compositions. Specifically, the invention is directed to a dentifrice composition with sodium fluoride having a low pH wherein the silica has a specific moisture content.
2. Description of Related Art
Low pH dentifrice compositions that contain abrasive silica are known in the art. Specifically, PCT Application WO 96/03109 to Warner-Lambert Company teaches an antiseptic, anticaries dentifrice having a pH of about 3.0 to about 5.5. The silicas used in the dentifrice include ZEODENT.RTM. 113 and SYLODENT.RTM. 750. The fluoride can be sodium monofluorophosphate, sodium fluoride and stannous fluoride.
U.S. Pat. Nos. 4,545,979 and 4,550,018 to Ambike et al. teach a dental hygiene composition in an acidic pH range of from 3.0 to 5.0. The fluorides used are sodium monofluorophosphate, sodium fluoride and stannous fluoride. The silica is ZEODENT.RTM. 113.
U.S. Pat. No. 5,094,843 to Mazzanobile et al. teaches an anti-plaque, anti-gingivitis toothpaste with a fluoride source and an antimicrobial agent consisting essentially of about 0.15% to about 0.80% thymol, about 0.15% to about 1.00% methyl salicylate, about 0.25% to about 0.80% eucalyptol and from about 0.15% to about 0.60% menthol. Mazzanobile et al. teach that the toothpaste will usually have a pH of from about 4 to about 8. The only example in Mazzanobile et al. has a pH of about 6.3. Mazzanobile et al. also disclose that Euthymol toothpaste has been sold in the United Kingdom. According to Mazzanobile et al. Euthymol toothpaste contains 0.12% thymol, 1.26% methyl salicylate, 0.07% menthol and 0.012% eucalyptol. Euthymol toothpaste has a pH of approximately 7.3-7.5. The fluorides taught in Mazzanobile include alkali metal fluoride, preferably sodium fluoride. The abrasives are generally described as silica dental abrasives such as those marketed under the tradenames "Zeodent" and "Slyodent."
Canadian Patent No. 834131 to Tisserand teaches a dentifrice preparation that has an acidic pH of about 3.8 to 5.8, optimally a pH of 4.0 to 5.5, and most preferably a pH of 4.0 to 4.8. Tisserand teaches using numerous fluoride sources including sodium fluoride. The abrasives are described as polishing agents including aluminum silicate and zirconium silicate.
The problem of poor stability of fluoride in silica containing, low pH dentifrice compositions is also known. For example, Prencipe et al., "Squeezing Out A Better Toothpaste", Chemtech, Dec. 5, 1995, pp. 38-42, teaches that sodium fluoride can be trapped by the silica at pH values significantly&lt;7.
U.S. Pat. No. 4,350,583 to Wason teaches a silica composition for use in a toothpaste that is highly compatible with fluoride, including sodium fluoride. The toothpaste has a pH of from about 4 to 8 when slurried with water in a 3:1 water/composition weight ratio.
While the prior art discloses toothpaste and other dentifrice compositions with silica and sodium fluoride at low pH, there is a need for dentifrice compositions wherein the silica is chosen to so as maximize the available fluoride.